Garlic is the bulb of Allium sativum L., native to West Asia and Central Asia, since Zhang Qian’s mission to the Western Regions in the Han Dynasty to bring garlic back to China to settle down, so far there have been more than 2,000 years of history. At present, China’s garlic production accounts for more than 70% of the world’s total output.

According to the color of the outer skin of the bulb, garlic can be divided into two kinds: purple garlic and white garlic. Purple-skinned garlic has few and large cloves with strong pungent flavor, while white-skinned garlic has two kinds of cloves, large and small, with lighter pungent flavor.

In this study, the chemical composition of garlic, the preparation method of the extract and its application in food processing were discussed, with a view to providing reference for the development and utilization of garlic and its extracts.

Chemical and nutritional composition of garlic

Garlic is rich in nutrients, containing thiamin, riboflavin, niacin, allicin, citral and selenium and germanium and other trace elements, containing volatile oil about 0.2%, the main component of the oil is allicin. Allicin has a bactericidal effect, is the garlic contained in allicin hydrolyzed by the action of garlic enzyme.

Garlic also contains some special physiologically active substances, such as superoxide dismutase, so that garlic has antibacterial and anti-inflammatory, anti-cancer, treatment and prevention of cardiovascular disease, improve the immune function of body cells and protect the liver and other physiological effects. Garlic is known as a “natural antibiotic” and is recommended by Time Magazine as one of the ten best nutritional foods.

Preparation of Garlic Extract

1.Garlic Extract

Garlic extract is a general term for the crude extract of garlic that is extracted with organic solvents or water after crushing. The main extract of garlic is allicin, the main component of which is diallyl sulfide, an extremely unstable organic sulfide, almost completely decomposed after 20 hours at room temperature (20 ℃), and the decomposition speed is accelerated by heat.

Therefore, it is difficult to extract and preserve allicin, which is one of the important components of garlic extract with anti-microbial effect.

2.Preparation of garlic extracts

At present, the main methods for extracting allicin are water vapor distillation, solvent extraction and supercritical CO2 extraction.

Among them, water vapor distillation method is low cost, simple equipment, good stability, is one of the commonly used methods; supercritical CO2 extraction method is safe, reliable, simple operation, widely used in food, medicine and other fields. Supercritical CO2 fluid extraction technology is a new type of extraction, separation technology, with no solvent residue, can better retain the active ingredients of raw materials and other advantages, is widely used in the food field, for the extraction, preparation of a variety of high value-added food.

Taking garlic as raw material, allicin was extracted by combining ethanol leaching and supercritical CO2 purification, which can realize the continuous supercritical CO2 extraction and purification operation of allicin.

Garlic is mixed with other seasonings to make a variety of sauces, giving the dishes a unique flavor. Garlic and salt, monosodium glutamate, sugar, etc. mixed into a light yellowish-white garlic sauce, can be used as a flavor plate; garlic and soybean paste, sweet noodle sauce, red pepper, sesame oil mixed into a sauce-colored sauce plate; garlic mixed with edamame, oyster sauce, ginger, etc. made into a light-brown garlic black bean sauce, in the mixing vegetables, stir-fry dishes in a wide range of applications; garlic mixed with chili sauce, cumin, sesame seed powder, black pepper, five-spice powder, sugar, etc. made of dilute paste of garlic mixed with water Barbecue sauce, taste fresh salty and slightly spicy, garlic aroma, especially suitable for meat and shells of cartilage seafood; garlic mixed with olive oil, salt, parsley and other minced to make a fresh and salty garlic bread sauce, can be spread on slices of baguette bread, baked with a better taste.

Garlic and its extracts in food processing applications

The pungent flavor of garlic is mainly used in cooking, especially in mixed dishes. In fact, the role of garlic in food processing and cooking is much more than that, it plays a unique role in food preservation, compound flavor mixing, sauce production.

1.Application in food preservation

Garlic has the role of disinfection and sterilization, enhance immunity. Chen Hongsheng et al. applied the antioxidant ability of garlic to the preservation process of cooled meat, through the determination of microbiological indicators and physical and chemical indicators, and combined with sensory evaluation to determine the preservation and antioxidant effect of different concentrations of garlic extract on cooled meat.

The experimental results showed that garlic extract at a concentration of 2% had good antibacterial and antioxidant effects on the cooled meat, and had little effect on the color of the meat. Li Tingting et al. studied the effect of garlic extract on the quality of refrigerated vegetable fishballs by adding different concentrations of garlic extract to vegetable fishballs and comparing the indexes (sensory indexes, microbiological indexes, chemical indexes, etc.) of each experimental group at 4 ℃ under refrigerated conditions.

The results showed that the best preservation effect was achieved when garlic extract was added at 200 mg/kg, which could extend the shelf life of fishballs for 7-8 days. After comparing the total bacterial counts, pH value, TBA, TVB-N and other quality indexes, it was found that garlic extract could effectively inhibit bacterial growth and slow down the oxidization and deterioration of proteins and fats in the process of preserving fishballs under refrigeration.

Zhao Mei et al. used shiitake mushrooms as raw materials and studied the effect of different concentrations of garlic extract on the preservation of shiitake mushrooms. The results showed that different concentrations of garlic extract could effectively inhibit the respiratory strength, cell membrane permeability, weight loss rate and decay index of shiitake mushrooms, and also reduce the changes in the appearance of shiitake mushrooms and delay the decay of shiitake mushrooms, among which, the best preservation effect was found with a material-liquid ratio of 1∶5 of the garlic extract.

Garlic extract not only has antibacterial and antiseptic effects, but also can regulate the physiological metabolism of fruits and vegetables, and maintain the good quality of fruits and vegetables. Feng Deming et al. applied the alcohol extract of allicin to soybean products to preserve freshness, and achieved good results.

2. Formation of unique aroma

Research has found that: garlic in 150 ~ 160 ℃ by oil stir-fry, containing sulfur ether compounds can form a special flavor and aroma, garlic broccoli, garlic ribs, garlic fish and shrimp and other cooking is the use of this feature.

Gao Xueqin and other use of fixed sulfur method to determine the effect of different cooking methods on allicin, the results show that the most suitable cooking method for garlic is microwave heating, the destruction of allicin is the largest frying cooking method.

The cooking method of “garlic explosion” is to heat garlic paste quickly under high oil temperature to produce flavor, and this method is often used in the cooking of leafy and stem vegetables, such as lettuce with garlic paste, amaranth with garlic paste, and oatmeal with garlic explosion, etc. The results showed that the most suitable cooking method for garlic is microwave heating, and the cooking method of deep-frying is the most destructive for allicin. Allicin and vegetables with the dishes have a unique flavor.

3. Sterilization and disinfection in cold dishes

Allicin and active ingredients contained in garlic ajoene, garlic oil in the sulfur ether and so on through the reaction with cysteine, can effectively inhibit the activity of hydrophobic enzyme or lipid metabolism and other substances, on a variety of pathogenic fungi, bacteria inhibition or killing effect.

Garlic in the antibacterial components of allicin and allicin on dysentery bacillus, typhoid fever bacillus and other pathogenic intestinal bacteria have a strong bactericidal effect, so it is widely used in the production of cold dishes, but in the process of using, the amount of garlic should not harm the food flavor, do not destroy the food flavor as a prerequisite.

4.Application in compound flavor

Research has found that the pungent flavor of allicin and soy sauce, vinegar, green onion, ginger, etc. with the formation of a variety of composite flavors, such as fish flavor, strange flavor, etc., to achieve better results.

Garlic and pickled chili peppers, soy sauce, salt, monosodium glutamate (MSG), sugar, ginger, etc., can form a compound fish flavor, salty, sweet, sour and spicy, onion, ginger and garlic aroma is strong.

Fish flavor type of wide range of applications, poultry dishes, livestock dishes, vegetarian dishes, poultry and egg dishes can be used, not only for fish-flavored shredded pork, fish-flavored phoenix claw and other hot dishes, but also for the production of cold dishes. Garlic mixed with soy sauce, salt, sugar, sesame oil and other seasonings can form a more special flavor – strange flavor.

Weird flavor is one of the first commonly used flavor type in Sichuan, because of the collection of many flavors in one, the balance of each flavor, harmony, so the word “weird” to praise the flavor of the wonderful, characterized by salty, sweet, numbing, spicy, acidic, fresh, fragrant and coordinated, and mostly used in cold dishes, such as weird bitter gourd, weird peanuts, and so on.

5. Mixed with other flavorings to make a variety of sauces

Qiao Aixia et al. on the ethanol extraction method for the extraction of allicin optimal process parameters for research, through the single-factor experiment and orthogonal test, the establishment of allicin extraction rate as the target value, to the enzyme temperature, enzyme time, extraction temperature, extraction time as a factor of the mathematical model for the full development and utilization of allicin to provide a scientific basis.

6. Deodorization and deodorization in the cooking of stinky and fishy raw materials
Many regions in our country in cooking with fishy, stinky raw materials will be added to garlic, such as garlic roasted catfish, garlic white meat, etc., in order to achieve the effect of deodorization, in addition to the effect of odor, because garlic in the allicin, pyruvic acid and ammonia, etc., can be dissolved to produce fishy odor of trimethylamine. Garlic puree mixed with salt and red chili oil to make garlic red oil sauce, mainly used for black beans after seasoning the white cooking dishes.

Garlic oil can be used to prepare sauces or make dishes, play a role in increasing the flavor and remove the odor. Garlic oil is obtained through the distillation of volatile essential oils, is a light red to light orange bright oily liquid, with a strong pungent odor and a special garlic aroma, this odor is generated by the decomposition of allicin in the enzyme alliinase, the main component is the diabase disulfide, methacrylene disulfide, and so on.

At present, the research of garlic in food processing mainly focuses on food preservation, dish flavoring technology, deep processing and utilization of the research is far from enough. The effective and safe natural active ingredients in garlic can be effectively developed and utilized, which has a far-reaching impact on the research and development of garlic health food and dishes.